As it is known, rapid prototyping or RP is the name given to a host of related technologies that are used to fabricate physical objects directly from CAD data sources. It regards in particular a rather recently developed technique that allows to obtain automatically the prototype of a mechanical component starting from its CAD drawing in a short time and with relatively low costs regardless of the geometry of the component.
The resulting prototype can be used in place of the actual component in performing tests for example of the photoelastic type, so as to determine the mechanical characteristics of said component.
It is also known that there are various rapid prototyping technologies, which in any case entail superimposing a plurality of layers of material that are mutually rigidly associated so as to obtain a model, optionally a scale model, of the actual component.
These technologies differ in the manner in which the layers of material are applied during prototype construction; in particular, each technology is based on a different physical principle, which determines the nature and state of final aggregation of the materials used.
The rapid prototyping process is organized into various steps: initially, the component being studied must be drawn with the aid of a three-dimensional solid or surface modeling system, so as to obtain a three-dimensional CAD model, which is then converted into a format that can be read by the prototyping machine, which is generally an STL (from “stereolithography”) format.
This conversion consists in approximating the surface of the model with a plurality of juxtaposed triangles, which are mutually adjacent so as to cover all of said surface.
The model in the STL format is sectioned, by the software that manages the rapid prototyping machine, with a plurality of parallel planes that are spaced by an appropriate thickness.
Each plane represents one of the layers of material that the machine subsequently superimposes; the contiguous layers bond with each other already during prototype construction.
Finally, it is possible to subject the resulting prototype to cleaning and finishing operations or to other kinds of treatment.
One of the known rapid prototyping technologies is constituted for example by the so-called SLS (Selective Laser Sintering) method, which is based on the consolidation of powders by means of a sintering process obtained by using a laser.
The machine used to perform this method is substantially constituted by a vertically movable platform on which the powder is deposited; said powder is retained inside the machine at a temperature just below its melting point, so as to constitute a layer of uniform thickness, which the laser strikes only at the region that forms the corresponding cross-section of the model to be produced, sintering it.
The platform then moves downward by an extent that corresponds to the thickness of the deposited material, and a new layer of powder is superimposed on the preceding one and sintered as described above, so as to solidify and bond with the underlying layer.
The process is repeated until the complete model is obtained.
The material currently used in rapid prototyping processes and in particular in the SLS method is generally constituted by a mixture of powders of the polyamide type, optionally with the addition of powders of various kinds that have a reinforcing effect.
Models obtained by using this material, while having a more than satisfactory quality, have still limited moduli of elasticity and low breaking loads.
During recent studies aimed at developing new sinterable materials that allow to optimize the mechanical characteristics of models produced by rapid prototyping, it has been found that the introduction of powdered aluminum in the above cited mixture increases the breaking load of the resulting models.
However, known sinterable powder mixtures are susceptible of further improvements, aimed in particular at improving the mechanical strength characteristics of the resulting models.